Control of cell growth is one of the most important aspect of an animal's physiology. The cells of an adult must divide frequently enough to allow tissues to remain in a steady state, and division must be stimulated at wounds or when special requirements are placed on a tissue. There must be many circulating cell-specific factors that signal individual cell types whether to divide or not. However, uninhibited cell growth results in tumors.
Malignant tumors can be differentiated from benign tumors by two major characteristics: invasiveness and spread. Malignant tumors do not remain localized and encapsulated, as do benign tumors. The malignant tumors invade surrounding tissues, invade the body's circulatory system, and set up areas of proliferation away from the site of their original appearance. Cancer cells have abnormal and unstable numbers of chromosomes, as well as many chromosomal abnormalities.
One of the major limitations of effective cancer chemotherapy is toxicity to normal tissues. Agents that are effective killers of neoplastic cells are usually also detrimental to normal cells, particularly to rapidly proliferative cells of the gastrointestinal tract and bone marrow. Some attempts have been made to deliver chemotherapeutics more directly to cancer cells by the use of antibody-drug conjugates, as described by Hurwitz in Optimization of Drug Delivery, Alfred Benzon Symposium 17, Editors, Hans Bundgaard et al., Munksgaard, Copenhagen, 1982. However, in this case, antibodies specific to the tumor must be used in order to provide the specificity of delivery required for this technique to be useful. More importantly, however, there has been no demonstration that this approach would be feasible in solid tumor systems, particularly in those which have a tendency to metastasize.
Nickel and certain of its diverse compounds are well known to be carcinogenic, and nickel carbonyl is the most carcinogenic of the inhaled nickel compounds. Inhalation of nickel carbonyl will produce lung cancer within a period of two years in Wistar rats, a species unusually resistant to lung cancer, and nickel subsulfide appears to have the greatest carcinogenic potential of the inorganic nickel compounds when injected into striated muscle or testes of experimental animals. Various soluble salts of diethyldithiocarbamate have been found to exert a detoxifying effect against the acute inhalation of lethal quantities of nickel carbonyl by warm-blooded animals, Sunderman et al., Annals of Clinical and Laboratory Science 14 (1):1-9, 1984. The soluble salts of diethyldithiocarbamate were found to inhibit carcinogenesis in rats chronically subjected to nickel subsulfide by muscular implantations (Sunderman et al., op. cit.). The diethyldithiocarbamates were found to bind nickel successfully, and met the criteria of a clinically useful metallic chelating agent: (1) non toxic; (2) relatively specific for the metal to be mobilized; and (3) capable of forming a stable excretable complex of the metal.
Sodium diethyldithiocarbamate has also been used as a potentiating agent for levamisole in treating cancer, Renoux, TIPS 248-249, 1981. Sodium diethyldithiocarbamate has been found, in high doses such as above 200 mg/kg, to potentiate barbital sleep, inhibit dopamine beta-hydroxylase and depress brain norepeniphrine levels. At doses of up to 600 mg/kg levels, sodium diethyldithiocarbamate induces retrograde amnesia of trained passive avoidance and cerebral seizure in the rat. This compound also prevents the development of chemically-induced diabetes. As a chelating agent, sodium diethyldithiocarbamate is used in the treatment of metal poisoning without toxic or untoward side effects at daily doses of 30-50 mg/kg body weight.
There has been no evidence of carcinogenicity of the diethyldithiocarbamate when administered in the feed for 104-109 weeks to rats and mice. The incidence of spontaneous tumors was lower in the dosed groups than in the corresponding control group. Additionally, the diethyldithiocarbamate was found to exert a protective effect against a variety of chemically-induced malignant tumors, and against ionizing radiation.
When used in immunostimulant doses of about 0.5-25 mg/kg, diethyldithiocarbamate evidences a unique influence on the immune system in inducing the recruitment of T cells for undifferentiated precursor cells. This influence is mediated through the increased synthesis of hormone-like factors active on the T-cell lineage. The diethyldithiocarbamate induces T cells to generate enhanced levels of cytotoxic activity and responses to alloantigens, macrophages and monocytes to participate in delayed-type hypersensitivity, resting T cells to develop suppressive activities, and B cells to secrete antibodies of the IgG class. These activities are probably associated with an increase in the number of Lyt-1+ T cells which provide the signal for help to increase the response of other cell subsets when needed. Diethyldithiocarbamate is devoid of direct influence on B cells, nonspecific polyclonal activity, and in vitro augmenting effects, and has no sensitizing or pyrogenic influence.
Perchellet et al. reported in Cancer Research 47: 6302-6309, 1987, that diethyldithiocarbamate injected intraperitoneally inhibits 12-O-tetradecanoylphorbol-13-acetate(TPA)-decreased glutathione peroxidase and TPA-induced ornithine decarboxylase activities in mouse epidermis in vivo. Diethyldithiocarbamate is more potent in inhibiting these effects of TPA than sixteen other antioxidants, free radical scavengers, thiol-containing compounds, and reduced glutathione level-raising agents, even though some of these treatments are applied directly to the TPA-treated skin. The powerful and long-lasting inhibitory effects of diethyldithiocarbamate affect both the first and second stages of skin tumor promotion.
However, because the diethyldithiocarbamate is injected intraperitoneally, it is likely that only very small fractions of the doses of diethyldithiocarbamate actually reach the target cells. Because there is a good correlation between polyamine and DNA synthesis, there is little doubt that the sequential induction of ornithine decarboxylase activity and macromolecule synthesis by TPA may be essential for the epithelial hyperproliferation associated with the later stages of skin tumor promotion. Moreover, the induction of epidermal DNA synthesis, but not ornithine decarboxylase activity, may be necessary for the conversion phase of skin carcinogenesis elicited when TPA is used as a stage 1 promoter. Since undisturbed DNA synthesis may be an essential component of several stages of tumor promotion, the efficacy of diethyldithiocarbamate against both the first and second stages of skin tumor promotion may be linked to its ability to inhibit DNA synthesis in conjunction with its antioxidant property.
There have been many reports in the prior art relating to the general concept of providing direct transport of an agent which is toxic to tumor cells directly to tumors having .beta. glucuronidase activity by conjugating the agent with glucuronic acid. Among such reports are Von Ardenne, M. et al., Agressologie, 1976, 176(5):261-264; East German Patent No. 122,386; German Offenlegungsschrift 22 12 014; Sweeney et al., Cancer Research 31:477-478, 1971; Baba et al., Gann. 69:283-284; and Ball, Biochem. Pharm 23:3171-3177 (1974).
Von Ardenne suggest broadly many types of aglycones which may be conjugated to glucuronic acid and will be active at the tumor site. There include, broadly, alkylating groups, antimetabolites, cytotoxins, membrane-active (lytic) groups, glycolysis stimulators, respiration inhibitors, inorganic and organic acids and cell cycle stoppers. The East German patent also suggests many such combinations, including 5-fluorouracil-glucuronide, aniline mustard-glucuronide and many others. The Offenlegungsschrift also mentions a large number of glucuronides. Sweeney et al. disclose the anti-tumor activity of mycophenolic acid-.beta.-D-glucuronides. Baba et al. note the anti-tumor activity of 5-fluorouracil-o-.beta.-D-glucuronide, and Ball discloses the anti-tumor activity of p-hydroxyaniline mustard glucuronide.
Rubin, in U.S. Pat. Nos. 4,337,760 and 4,481,195, discloses methods for treating tumors having high .beta.-glucuronidase activity with glucuronides with aglycones toxic to the tumor cells with great safety toward the rest of the body by first administering an alkalinizing agent in an amount sufficient to maintain the pH level of non-tumor tissues at approximately 7.4 during the glucuronide treatment to inactivate .beta.-glucuronidase activity in the rest of the body. Thus, the toxic agent is directed only to the cancer cells, as opposed to all of the healthy cells of the body, since the aglycone is only released at the cancer site. Tumors having high glucuronidase activity can be identified by assaying tumor cells obtained in a biopsy for .beta.-glucuronidase activity, or by administering a glucuronide whose aglycone has been labelled with a radioactive isotope. If upon a full body scan it is found that the radioisotope is accumulated at any specific areas of the body, this will indicate not only the location of the tumor but the fact that the tumor has sufficient .beta.-glucuronidase activity to deconjugate the glucuronide.
Borch, in U.S. Pat. No. 4,426,372, discloses that the toxicity of platinum (II) compounds used for treating tumors can be countered by administering dithiocarbamic compounds parenterally in a timely fashion. The cellular DNA is first exposed to platinum (II), and then the dithiocarbamic compound is administered. The dithiocarbamic compound is administered within six hours of platinum administration. The mode of administration of the dithiocarbamate is important, because acidic aqueous media, conjugating sugars, uronates, glycosides, liver tissue and other media or agents encountered in living biological systems can inactivate dithiocarbamic toxicity inhibitors long before the inhibitors can bind to the platinum. In addition, it has been found that alkali metal dithiocarbamates are sufficiently powerful platinum-binding compounds to dislodge the platinum from DNA/Pt(II) complexes formed in vitro.
The dithiocarbamates are also well known chelating agents for other metals such as zinc and copper.